1. Field of Application
The present invention relates to an image processing apparatus for processing images that are successively captured by an onboard camera of a vehicle and are affected by fog, with the apparatus generating corresponding restored images having effects of the fog substantially removed. The invention further relates to a driver support apparatus which utilizes the restored images.
2. Description of Related Art
Types of driver support apparatus are known whereby an onboard camera on a vehicle captures successive images of a region ahead of the vehicle, with the resultant images being displayed directly or after having been subjected to image processing. The images may be displayed to the driver and/or processed to detect objects appearing in them, with these being referred to in the following as target objects. The image processing results can be used to ascertain the road conditions in which the vehicle is travelling and to detect the presence of target objects which require caution, and so can be used in various ways to assist the driver in controlling the vehicle.
It has been proposed (for example in Japanese patent application first publication No. 2003-067755, referred to in the following as reference document 1) to use Kalman filter processing of images, in a driver support apparatus that incorporates an image processing apparatus. The purpose of using Kalman filter processing is to track specific image contents that appear in successive images captured by an onboard camera of the vehicle. Such specific image contents can for example be an edge of a white line on the road surface, specific regions of high luminance in the image, etc.
However the camera will in general be sensitive only to light that is within the visible spectrum. Hence, when the vehicle is being driven in a region affected by fog, the camera as well as the vehicle driver will experience reduced visibility of the surroundings of the vehicle. That is to say, there will be a reduced degree of variations in luminance values of objects appearing in images captured by the camera, so that the images will become low in contrast and blurred. It thereby becomes difficult for specific parts of successive images to be tracked. Thus it becomes difficult to detect specific objects in the processed output images, so that it may no longer be possible to provide a sufficient degree of driver support.
With an another type of apparatus (for example as described in Japanese patent application first publication No. 6-113308, referred to in the following as reference document 2), a system is utilized in which variations in density of fog are judged, and a currently captured image is adjusted based upon the positions of high-luminance regions in the image and upon an image which was captured immediately prior to time at which the fog became dense. The resultant adjusted image is displayed by the apparatus.
However with the apparatus of reference document 2, if a condition of thick fog continues for some time, then the actual surroundings of the vehicle may become substantially different from those prior to the time at which the fog started to become dense. Thus, an image that was captured prior to the fog becoming dense may not accurately correspond to the current environment of the vehicle, and so cannot be used as a reliable reference image. Hence if there are no objects of sufficiently high luminance in images that are captured during the condition of dense fog, the apparatus cannot function effectively.